DESCRIPTION (taken in part from the application's abstract) The proposed studies are designed to address the hypothesis that the NH4-terminal segment of the alpha-subunit of the Na-K-ATPase interacts with other cytoplasmic domains of the same subunit to modulate enzyme activity. Site-directed mutagenesis will be used to identify amino acids that are phosphorylated by protein kinase C (PKC); phorbol 12-myristate 13-acetate (PMA) stimulation has been shown to increase the affinity of the enzyme for intracellular Na (sodium), presumably via PKC phosphorylation. Cross-linking reagents will be used to identify cytoplasmic domains that interact with the NH-terminus of the alpha-subunit. The effect of phosphorylation on partial reactions of the Na-K-ATPase will be determined to attempt to define mechanisms of hormonal regulation of the enzyme. The ultimate aim is to understand molecular mechanisms of action of the Na-K-ATPase and thereby define pathophysiology of cardiovascular diseases potentially caused by dysfunction of this critical enzyme.